CN116522499A - Vehicle body front end structure design method based on thin-wall lattice filling structure - Google Patents
Vehicle body front end structure design method based on thin-wall lattice filling structure Download PDFInfo
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Abstract
The invention provides a vehicle body front end structure design method based on a thin-wall-lattice filling structure, which is characterized by comprising the following steps of: comprising the following steps: step 1: aiming at the front end structure of the new energy automobile, determining a design domain and a non-design domain according to the arrangeable space, and establishing a typical load working condition for load application; step 2: converting the solving of the multi-objective topological optimization problem into the solving of the single-objective optimization problem by adopting a flexibility weighting method, and carrying out multi-objective topological optimization solving by utilizing a solver; step 3: the structural reconstruction design is carried out on the topological optimization result of the front end structure of the vehicle body; step 4: constructing a solid unit model and a beam-shell composite unit model based on a thin-wall lattice filling structure; step 5: and (3) performing simulation performance verification by using a finite element method, and performing deformation mode analysis of the structural reconstruction design. The method combines the additive manufacturing process to realize the integrated design and manufacture of the thin-wall lattice filling structure, and provides a high-precision simulation modeling method corresponding to the model.
Description
Technical Field
The invention relates to the related field of structural optimization design methods, in particular to a method for designing a front end structure of a vehicle body based on a thin-wall lattice filling structure.
Background
The thin-wall-filled structure is typically composed of an outer dense material thin wall and an inner void-filling material. The thin wall of dense material provides a reliable boundary for the internal pore filling material while maintaining the external morphology of the overall structure. The thin wall of the compact material and the internal filling structure can cooperatively bear and influence the mechanical property and the failure rule of the whole structure through the topological configuration of the compact material. The thin wall-filled structure features make it exhibit excellent properties and light weight levels such as high specific stiffness, high specific strength, excellent sound absorption and energy absorption properties, etc. Compared with the traditional structure, the thin-wall filling structure can be designed through the cooperation of the integral structure and the filling structure, so that the mechanical property and the light weight level are improved to the greatest extent. With the diversification development of lightweight design of structures, simple configuration under single working condition cannot meet the demand. The thin-wall lattice filling structure is combined with topology optimization to obtain complex configurations under more conditions, namely the thin-wall lattice filling structure based on the topology optimization, and the thin-wall lattice filling structure is a future development trend of the thin-wall lattice filling structure. And the widespread use of additive manufacturing technology in recent years has made it possible to manufacture complex structures, which greatly expands the design space of the structure.
The front end structure of the automobile body is a complex system component of integrating a plurality of components outside the automobile and mainly plays a role in connecting the front end of the automobile and integrating functions. In recent years, with rapid development of manufacturing technology, the front-end structure of an automobile has been developed toward integration, weight reduction, and the like. In the conceptual design stage, the optimal layout of the materials is obtained through topological optimization, so that the structural performance is ensured, and meanwhile, the light weight level is improved to the maximum extent. Particularly, with the development of additive manufacturing technology, a manufacturing guarantee is provided for manufacturing a light-weight ultra-light structure for a new energy automobile.
Due to the energy density of the power battery, the new energy automobile has more urgent requirements on light weight, the topological optimization and additive manufacturing are comprehensively utilized, the front end structure of the thin-wall-lattice filling type new energy automobile is designed and manufactured, the comprehensive potential of materials and structures can be fully excavated, the realization of high-performance ultra-light weight is facilitated, and a new thought is provided for the innovative design of the structure of the future ultra-light new energy automobile.
Disclosure of Invention
The invention aims to provide a vehicle body front end structure design method based on a thin-wall lattice filling structure by taking a vehicle body front end structure frame of a new energy vehicle as an object. Firstly, according to 7 front-end structure load working conditions, obtaining an optimal force transmission path based on topological optimization of a variable density method; then, based on the optimal force transmission path, reconstructing by combining with the optimization of the rod diameter size to obtain a thin-wall-lattice filling type integrated front-end vehicle body structure; finally, the torsional rigidity and the bending rigidity of the structure are verified through simulation. By adopting the thin-wall lattice filling structure, the light weight level can be effectively improved while the excellent mechanical property is ensured, and the weight reduction ratio can reach 85.51 percent.
In order to achieve the above purpose, the specific technical scheme of the invention is as follows:
the invention provides a vehicle body front end structure design method based on a thin-wall-lattice filling structure, which comprises the following steps:
step 1: aiming at the front end structure of a certain new energy automobile, determining a design domain and a non-design domain according to an arrangeable space, establishing a finite element grid, selecting 7 typical load working conditions for load application, applying boundary conditions, setting manufacturability constraint, and carrying out initialization assignment on optimization parameters;
step 2: converting the solving of the multi-objective topological optimization problem into the solving of the single-objective optimization problem by adopting a flexibility weighting method, establishing a mathematical optimization model of the single-objective topological optimization problem, and carrying out multi-working condition topological optimization solving by utilizing a solver;
step 3: carrying out structural reconstruction design on the topological optimization result of the front end structure of the vehicle body in the step 2, then carrying out further size optimization on the structure rod diameter, and filling a solid model with the optimized rod diameter size by utilizing three-dimensional modeling software to obtain a concise geometric configuration and improve the integration degree;
step 4: and constructing a solid unit model and a beam-shell composite unit model based on the thin-wall lattice filling structure.
Step 5: performing simulation performance verification by using a finite element method, performing deformation mode analysis of a structural reconstruction design, and performing mechanical performance evaluation on the reconstructed structure;
the invention has the beneficial effects that:
(1) The invention combines the additive manufacturing process to realize the integrated design and manufacture of the thin-wall lattice filling structure, and provides a high-precision simulation modeling method corresponding to the model.
(2) The invention utilizes the design domain of the front end structure of a certain type of automobile body as the basis to carry out multiplexing Kuang Tapu optimization, and carries out reconstruction design on the obtained force transmission path, thereby realizing the application of the thin-wall lattice filling structure in the front end structure of the automobile body. Under the condition of extremely high weight reduction ratio, the obtained structure still keeps higher level of rigidity, which shows that the thin-wall-lattice filling structure based on topological optimization has excellent material utilization rate and is enough to meet the design requirement under multiple working conditions.
(3) In addition, the invention explores a novel design method with light structure, and explores and verifies the effectiveness and feasibility of the design method from multiple aspects by expanding the complexity of geometric shapes and load working conditions.
Drawings
FIG. 1 is a diagram of a design domain boundary reference in the present invention;
FIG. 2 is a design domain actual model reference in the present invention;
FIG. 3 is a finite element mesh model of a design domain in the present invention;
FIG. 4 is a finite element model boundary setup reference of FIG. 3 according to the present invention;
FIG. 5 is a typical load condition of the present invention;
FIG. 6 is a plot of weighted compliance as a function of iteration number for an optimization process;
FIG. 7 is a topology optimization resulting structure;
FIG. 8 is a high density region of the topology optimization result of FIG. 7 in accordance with the present invention;
FIG. 9 is a front end reconstruction of FIG. 7 in accordance with the present invention;
FIG. 10 is a diagram of the internal lattice filling structure model of FIG. 9 according to the present invention;
FIG. 11 is a graph of displacement deformation and stress distribution under torsional conditions of FIG. 9 according to the present invention;
FIG. 12 is a graph of displacement deformation and stress distribution under lateral bending conditions of FIG. 9 according to the present invention;
FIG. 13 is a graph showing the displacement deformation and stress distribution of FIG. 9 under vertical bending conditions according to the present invention.
Detailed Description
In order to better understand the technical solutions of the present application, the present invention will be further described in detail below with reference to the drawings and the embodiments.
The terms of upper, lower, left, right, front, rear, and the like in the present application are established based on the positional relationship shown in the drawings. The drawings are different, and the corresponding positional relationship may be changed, so that the scope of protection cannot be understood.
The embodiment provides a vehicle body front end structure design method based on a thin-wall-lattice filling structure, which specifically comprises the following steps:
step 1: aiming at the front end structure of a certain new energy automobile, determining a design domain and a non-design domain according to an arrangeable space, establishing a finite element grid, selecting 7 typical load working conditions for load application, applying boundary conditions, setting manufacturability constraint, and carrying out initialization assignment on optimization parameters;
the solid unit model and the beam-shell composite unit model based on the thin-wall lattice filling structure are constructed as follows:
the design domain of the front end structure base design of the vehicle body is constructed as follows:
a geometric model of a certain car body is extracted, and only the front end part of the study is reserved for the car body model. At present, no commercial software capable of directly carrying out thin-wall-lattice filling structure optimization design exists, so that solid models are utilized to carry out lattice filling cells to carry out uniform filling by utilizing three-dimensional modeling software.
In order to ensure the original wheel, suspension and trunk configuration of the automobile, the design domain takes the main frame and the firewall as connecting surfaces, comprises the auxiliary frame and the front end anti-collision beam, and is symmetrical about the xOz plane as a whole. The front end design domain of the vehicle body and the firewall are set to be a common node, and full constraint of six degrees of freedom is set above and below the firewall to be used as a boundary condition shared by all load working conditions. In this embodiment, its boundary references are as shown in fig. 1. Considering that the whole structure is symmetrical about the xOz plane, the actual volume of the obtained design domain is 2.98X10 8 mm 3 As shown in fig. 2.
In order to show the details of the optimized structure as much as possible, the mesh size of the design domain is set to 10mm and is a regular hexahedral solid mesh, wherein the front end design domain has 652684 mesh units and the firewall has 61072 mesh units, as shown in fig. 3. The front end design domain of the vehicle body and the firewall are set to be a common node, and full constraint of six degrees of freedom is set above and below the firewall as a boundary condition shared by all load working conditions, as shown in fig. 4.
Since forces are transferred to the body structure by means of wheels and wheel suspensions, loads associated with travel and handling are often applied to the connection locations of the main and sub frames and suspensions, while loads associated with examining the bending stiffness of the body front end structure as a whole are applied to the connection locations of the impact beam and the side rail. In the original design, the connection of the suspension and the main and auxiliary vehicle bodies and the connection of the anti-collision beam and the longitudinal beam are realized through bolts, and in order to ensure the connection of the three groups of load application points and the whole design domain, units near the load application positions are isolated from the design domain independently to serve as non-design domains.
The load working conditions of the front end structure of the automobile are set as follows: 7 more typical load conditions were chosen and all load conditions were statically linear, including: torsional rigidity working condition, lateral rigidity working condition, upward bending working condition, upper right wheel suspension working condition, suspension upper compression working condition, lower right wheel suspension working condition and auxiliary frame compression working condition.
In the embodiment, a soft weighted method is adopted to convert solving the multi-objective topological optimization problem into solving the single-objective optimization problem, and a mathematical optimization model is established; the 7 more typical load conditions are shown in fig. 5, and are specifically defined as follows:
(a) Torsional stiffness operating mode: two equal and opposite concentrated forces parallel to the z axis act on two connecting positions of the upper part of the suspension and the main body respectively;
(b) Lateral stiffness conditions: the two concentrated forces with the same magnitude and direction are respectively applied to two connecting positions of the anti-collision beam and the longitudinal beam along the negative direction of the y axis;
(c) Bending up working condition: the two concentrated forces with the same magnitude and direction are respectively applied to two connecting positions of the anti-collision beam and the longitudinal beam along the positive direction of the z-axis;
(d) Upper right wheel suspension operating mode: a concentrated force acts on the connection point of the upper part of the suspension and the main frame at the right side and is led into the vehicle body;
(e) Suspension upper compression conditions: the two concentrated forces parallel to the y axis with equal load and opposite direction respectively act on the two connecting positions of the upper part of the suspension and the main body;
(f) Lower right wheel suspension operating mode: a concentrated force acts on the connection point of the lower part of the suspension and the main frame at the right side and is led into the vehicle body;
(g) Compression working condition of auxiliary frame: two equal but opposite concentrated forces parallel to the y-axis act on the two connection locations of the lower part of the suspension to the main body, respectively.
Since the structure is considered symmetrical about the xOz plane, loads symmetrical about that plane for load conditions (b) and (d) are not applied. If the symmetrical working conditions are repeatedly applied, the repeated calculation of the weights for the working conditions which are substantially the same in response to the final calculation structure can be caused, so that the optimization result is influenced, and the calculation time of the overall optimization is increased. Finally, considering the manufacturability of additive manufacturing, carrying out manufacturability constraint setting on the finite element model. The filling structure is equivalent to a homogeneous isotropic material under a typical load working condition, and a thin-wall envelope is generated at the outer side of a force transmission path, so that a structure with excellent mechanical properties can be obtained.
In this embodiment, two material parameters are adopted in the topology optimization design:
(1) Aluminum, with an elastic modulus of 66444.8MPa, a Poisson ratio of 0.33, and a density assigned to the whole design domain unit;
(2) The carbon structural steel has an elastic modulus of 196000MPa, a Poisson ratio of 0.33 and a density assigned to the whole firewall unit.
Step 2: converting the solving of the multi-objective topological optimization problem into the solving of the single-objective optimization problem by adopting a flexibility weighting method, establishing a mathematical optimization model of the single-objective topological optimization problem, and carrying out multi-working condition topological optimization solving by utilizing a solver;
the multi-objective topology optimization method using compliance weighting is as follows:
find x＝{x 1 ,x 2 ,...,x i } T ,i＝1,2,...,n
s.t.KU e ＝F e
x min ≤x i ≤x max
wherein x= { x 1 ,x 2 ,...,x i } T The relative density of each unit of the design domain of the front end structure of the vehicle body is corresponding to the design variable vector, and n is the total number of the load working conditions of the front end structure of the vehicle body; w (w) e The weight factor of the e working condition; c e (x) The compliance for the e-th condition; k is the overall stiffness matrix; f (F) e And U e The load and displacement matrix corresponding to the e-th working condition are respectively adopted; v i The unit volume after optimization; v (V) 0 To optimize the total volume of the front end structure of the front vehicle body; f is the volume fraction; x is x min Is the lower limit of the design variable; x is x max Is the lower limit of the design variable. Based on the finite element model and the topological optimization modelThe following parameters are set for multi-working condition topology optimization solving:
the volume fraction constraint in the topology optimization model is set to 0.08, the minimum cell density is set to 0.01, and the relative convergence criterion is set to 0.001. Further, to ensure manufacturability of the topology optimization result, the minimum size constraint is set to 30mm and the maximum size constraint is set to 60mm.
Step 3: and (3) carrying out structural reconstruction design on the topological optimization result of the front end structure of the vehicle body in the step (2), further optimizing the size of the structural rod diameter, and filling the entity model with the optimized rod diameter size by utilizing three-dimensional modeling software to obtain a concise geometric configuration.
The change curve of the weighted flexibility along with the iteration number in the whole optimization process is shown in fig. 6, and when the iteration number reaches 110, the convergence condition is reached. In the optimization result, the density interval unit of 0.3-1.0 accounts for 8.0% of the designed domain volume, and the density interval unit is consistent with the constraint of the optimization volume fraction, so that the displayed density threshold value is set to be 0.3, and the obtained structure is shown in fig. 7.
In order to better determine the force transmission path of the front end structure of the vehicle body, a high-density region which shows the topology optimization result is emphasized as a main reference of the structural reconstruction design, as shown in fig. 8. The vehicle body front end structure reconstruction design complies with the following principles:
(1) The connection between a suspension and a bumper in the original new energy automobile model and the improved design structure is ensured, and the interference between wheels and the structure is avoided;
(2) The connection between the front end structure of the vehicle body after the improvement design and the original vehicle body frame is ensured;
(3) The structures with smaller volumes and complex geometric configurations are combined, and important characteristics in the force transmission path are reserved.
In the optimization result, the percentage of the units of different density intervals accounting for the original design domain volume is analyzed, wherein elements in the density interval of 0.3-1.0 account for 80% of the design domain volume in total, and the constraint of the optimization volume fraction is kept consistent, so that the displayed density threshold value is set to be 0.3. On the basis, the size optimization method is utilized to optimize the size of the rod diameter of the high-density area model, the parameters such as the cross section area of the beam unit, the thickness of the shell unit and the like are changed to enable the parameters to meet the mechanical property requirements of the structure, and finally the front end reconstruction structure of the vehicle body, which ensures the light weight level, is obtained. The obtained front end reconstruction design of the vehicle body is shown in fig. 9, and the thin-wall lattice filled internal structure of the front end structure of the vehicle body is shown in fig. 10;
step 4: and constructing a solid unit model and a beam-shell composite unit model based on the thin-wall lattice filling structure.
Compared with the traditional topology optimization method with single material property, the topology optimization method with the thin-wall filling structure generates thin-wall layers with different material properties on the periphery of a main force transmission path and a bearing configuration, so that the stability of the whole structure is greatly enhanced, and meanwhile, the energy absorption capacity, the deformation mode and the like are greatly influenced. Filling structure and thin-wall entity layer
The topological optimization method of the thin-wall uniform filling structure is characterized in that the filling structure is equivalent to a homogeneous isotropic material, a thin-wall envelope is generated at the outer side of a force transmission path, a structure with excellent mechanical properties can be obtained, and a mathematical model is as follows:
s.t.KU＝F
g(μ)＝M(μ)/M * -f mass ≤0
wherein c is compliance; mu is a design variable; k is the overall stiffness matrix; u and F are the overall displacement and force vectors; m (mu) is the optimized material quality; m is M * Is the maximum value of the set material quality; f (f) mass Is the mass fraction; the expression g (μ) indicates that the actual mass fraction of the solid material and the filler material is less than the preset mass fraction maximum.
The different material characteristics not only increase the degree of freedom of design, but also provide a new research idea for the design of the multifunctional composite structure. The lattice cells appear microscopically as microstructures while macroscopically can be seen as homogeneous materials, i.e. there is a length-scale separation between the cell scale and the macrostructure scale. Thus, the unit cells of the lattice structure can be modeled as volumes comprising homogeneous material, i.e. representative volume units, and the mechanical behavior of the lattice structure on a macroscopic scale can be described by equivalent homogeneous properties of the representative volume units, which depend on the parent material properties and cell geometry and parameter settings. The lattice structure can realize the change of various performances in a specific design space by changing the geometric configuration and corresponding parameters of the structure under the same parameters of the parent metal. In the invention, the same entity material as the thin-wall structure is filled in the key bearing position of the front end structure of the vehicle body, so that the topology optimization method of the thin-wall mixed filling structure is realized, the rigidity of the structure can be effectively improved, the stress maximum value is reduced, and the mathematical model is as follows:
s.t.KU＝F
0≤μ 1 ≤1
0≤μ 2 ≤1
wherein mu is 1 And mu 2 Two design variables in the same design domain refer to the mass of the solid material and the filler material respectively and the mass of the solid material and the filler material respectively; m (mu) is the optimized material quality; m is M * Is the set maximum value of the material quality. f (f) mass1 And f mass2 The mass fraction maximum value of the solid material and the filling material is preset; expression g 1 (μ 1 ,μ 2 )、g 2 (μ 1 ,μ 2 ) Representation ofThe actual mass fraction of the solid material and the filling material is smaller than the maximum value of the preset mass fraction; c (mu) 1 ,μ 2 ) Is soft; k is the overall stiffness matrix; u and F are the overall displacement and force vectors. And defining an interpolation function of the mass density and the rigidity of the thin-wall-mixed filling structure topology optimization method by combining a two-step filtering method.
Step 5: performing simulation performance verification by using a finite element method, performing deformation mode analysis of a structural reconstruction design, and performing mechanical performance evaluation on the reconstructed structure;
further, in step 5, the size optimization method is used to optimize the size of the rod diameter for the high-density region model. In the optimization process, parameters such as the cross section area of a beam unit, the thickness of a shell unit and the like are changed to enable the unit properties of the structure to meet the mechanical property requirements of the structure, and finally, the front end reconstruction structure of the vehicle body, which ensures the light weight level, is obtained.
Further, in step 5, the verification of the simulation performance is as follows:
in order to enable the simulation analysis to be closer to the force transmission form of the thin-wall lattice filling structure, and comprehensively consider the calculation cost, a composite unit finite element model combining a shell unit and a solid unit is adopted, wherein the shell unit represents a thin-wall layer, and the solid unit represents an internal filling structure. The material parameters of the structure adopt the equivalent elastic modulus obtained by the quasi-static compression experiment of the thin-wall lattice filling structure, and three filling structures with different relative densities are adopted for simulation contrast analysis. Simulation verification shows that the torsion working condition, the lateral bending working condition and the vertical bending working condition are selected. The whole structure presents a reasonable deformation mode and symmetry under three working conditions.
Wherein the stress distribution of the torsional mode is concentrated at the constraint applying location at the trailing end of the structure, the torsional load loading is more similar to cantilever Liang Gongkuang. The stress of the lateral bending and vertical bending working conditions is distributed on the rod after reconstruction, which shows that the structure obtained by the reconstruction modeling has very obvious influence on the structural deformation under the two working conditions.
The deformation mode and stress distribution of the front end structure of the vehicle body after the design is restructured by qualitative analysis, and simulation results with the relative density of 0.082 are selected for display, as can be seen from fig. 11-13, the whole structure presents a reasonable deformation mode and symmetry under three working conditions. Wherein the stress distribution of the torsional mode is concentrated at the constraint applying location at the trailing end of the structure, the torsional load loading is more similar to cantilever Liang Gongkuang. The stress of the lateral bending and vertical bending working conditions is distributed on the rod after reconstruction, which shows that the structure obtained by the reconstruction modeling has very obvious influence on the structural deformation under the two working conditions.
For quantitatively analyzing the front end structure of the vehicle body after the improvement design, the rigidity under the three working conditions is calculated for comparison analysis. The calculated expression of torsional stiffness is:
wherein K is t The unit is kN multiplied by m/deg for torsional rigidity; f (F) t To concentrate force under torsion condition, F t Taking 1000N; l is the distance of the load applying point along the y axis, and L is 0.9m; u (u) t The absolute value of the maximum displacement difference value of the left side and the right side is expressed in mm.
The calculation expression of the bending stiffness is:
wherein K is b Is bending stiffness in N/mm; f (F) b To concentrate the sum of forces under bending conditions, F b Taking 2000N; u (u) b Is the maximum displacement of the structure in mm. The front end frame structure of the automobile model used in this chapter has a volume of about 0.012m 3 At a density of 7980kg/m of steel 3 Calculating the mass m 0 95.76kg, so that the weight reduction ratio W of the thin-wall lattice filling structure L The computational expression is:
wherein m is 0 Before optimizingMass of original structure, m d Is the mass of the thin-wall lattice filling structure.
Table 1 shows the weight reduction ratios for three different relative density filling modes, and the resulting stiffness index under three conditions. It can be seen that the overall structure has good stiffness even at a weight loss ratio of 85.51%. In addition, the increase of the relative density has obvious influence on all three rigidity indexes, and the amplitude change is approximately linear, so that the method has a direct guiding effect on the selection of the relative density in practical engineering application.
The shapes of the various components in the drawings are illustrative, and do not exclude certain differences from the actual shapes thereof, and the drawings are merely illustrative of the principles of the present application and are not intended to limit the present application.
Although the present application is disclosed in detail with reference to the accompanying drawings, it is to be understood that such descriptions are merely illustrative and are not intended to limit the application of the present application. The scope of the present application is defined by the appended claims and may include various modifications, alterations, and equivalents to the invention without departing from the scope and spirit of the application.
Claims (6)
1. A design method of a front end structure of a vehicle body based on a thin-wall lattice filling structure is characterized by comprising the following steps of: the method comprises the following steps:
step 1: aiming at the front end structure of the new energy automobile, a design domain and a non-design domain are determined according to the arrangeable space, a finite element grid is established, material setting is carried out, 7 typical load conditions of torsional rigidity working conditions, lateral rigidity working conditions, upward bending working conditions, upper right wheel suspension working conditions, suspension upper compression working conditions, lower right wheel suspension working conditions and auxiliary frame compression working conditions are selected for load application, boundary conditions are applied, manufacturability constraint is set, and initialization assignment is carried out on optimized parameters;
step 2: converting the solving of the multi-objective topological optimization problem into the solving of the single-objective optimization problem by adopting a flexibility weighting method, establishing a mathematical optimization model of the single-objective topological optimization problem, and carrying out multi-working condition topological optimization solving by utilizing a solver;
step 3: and (3) carrying out structural reconstruction design on the topological optimization result of the front end structure of the vehicle body in the step (2), further optimizing the size of the structural rod diameter, and filling the entity model with the optimized rod diameter size by utilizing three-dimensional modeling software to obtain a concise geometric configuration.
Step 4: constructing a solid unit model and a beam-shell composite unit model based on a thin-wall lattice filling structure;
step 5: and (3) performing simulation performance verification by using a finite element method, performing deformation mode analysis of the structural reconstruction design, and performing mechanical performance evaluation on the reconstructed structure.
2. The method for designing a front end structure of a vehicle body based on a thin-wall lattice filling structure according to claim 1, characterized in that: in step 1, the design domain is constructed as follows for the structure foundation design of the front end of the vehicle body: extracting a geometric model of the vehicle body, reserving only the front end part of the study on the geometric model of the vehicle body, and uniformly filling lattice filling cells of the physical model by utilizing three-dimensional modeling software; the design domain takes the main frame and the fire wall as the connecting surfaces, comprises the auxiliary frame and the front end anti-collision beam, sets the front end design domain of the vehicle body and the fire wall as a common node, and sets the full constraint of six degrees of freedom above and below the fire wall as the boundary condition shared by all load working conditions.
3. The method for designing a front end structure of a vehicle body based on a thin-wall lattice filling structure according to claim 1, characterized in that: in step 2, the multi-objective topology optimization method using compliance weighting is as follows:
find x＝{x 1 ,x 2 ,...,x i } T ,i＝1,2,...,n
s.t.KU e ＝F e
x min ≤x i ≤x max
wherein x= { x 1 ,x 2 ,...,x i } T The relative density of each unit of the design domain of the front end structure of the vehicle body is corresponding to the design variable vector, and n is the total number of the load working conditions of the front end structure of the vehicle body; w (w) e The weight factor of the e working condition; c e (x) The compliance for the e-th condition; k is the overall stiffness matrix; f (F) e And U e The load and displacement matrix corresponding to the e-th working condition are respectively adopted; v i The unit volume after optimization; v (V) 0 To optimize the total volume of the front end structure of the front vehicle body; f is the volume fraction; x is x min Is the lower limit of the design variable; x is x max Is the lower limit of the design variable. Based on the finite element model and the topology optimization model, topology optimization parameters are set for multi-task topology optimization solution.
4. The method for designing a front end structure of a vehicle body based on a thin-wall lattice filling structure according to claim 1, characterized in that: in step 4, filling the same solid material as the thin-wall structure in the key bearing position to realize the topology optimization method of the thin-wall-mixed filling structure, which can effectively improve the rigidity of the structure and reduce the maximum stress, and the mathematical model is as follows:
s.t.KU＝F
0≤μ 1 ≤1
0≤μ 2 ≤1
wherein mu is 1 And mu 2 Two design variables in the same design domain refer to the mass of the solid material and the filler material respectively and the mass of the solid material and the filler material respectively; m (mu) is the optimized material quality; m is M * Is the maximum value of the set material quality;and->The mass fraction maximum value of the solid material and the filling material is preset; expression g 1 (μ 1 ,μ 2 )、g 2 (μ 1 ,μ 2 ) Indicating that the actual mass fraction of the solid material and the filling material is smaller than the maximum value of the preset mass fraction; c (mu) 1 ,μ 2 ) Is soft; k is the overall stiffness matrix; u and F are the overall displacement and force vectors.
5. The method for designing a front end structure of a vehicle body based on a thin-wall lattice filling structure according to claim 1, characterized in that: in step 5, the size optimization method is utilized to optimize the size of the rod diameter of the high-density area model, and in the optimization process, the vehicle body front end reconstruction structure ensuring the light weight level is obtained by changing the unit attribute of the structure.
6. The method for designing a front end structure of a vehicle body based on a thin-wall lattice filling structure according to claim 5, characterized in that: in step 5, the mechanical properties of the reconstructed structure are evaluated as follows:
for quantitatively analyzing the front end structure of the vehicle body after the improvement design, the rigidity under different working conditions is calculated for comparison analysis, and the calculation expression of the torsional rigidity is as follows:
wherein K is t The unit is kN.m/deg for torsional rigidity; f (F) t Is the concentrated force under the torsion working condition; l is the distance along the y-axis of the load application point; u (u) t The absolute value of the maximum displacement difference value of the left side and the right side is in mm;
the calculation expression of the bending stiffness is:
k in the formula b Is bending stiffness in N/mm; f (F) b To concentrate the sum of forces under bending conditions, F b Taking 2000N; u (u) b Is the maximum displacement of the structure in mm.
Weight reduction ratio W of thin-wall lattice filling structure L The computational expression is:
wherein m is 0 To optimize the quality of the prepro structure, m d Is the mass of the thin-wall lattice filling structure.
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